The present invention relates generally to semiconductor laser diodes. In particular, the present invention is a II-VI laser diode having a buried-ridge waveguide, and a method for fabricating the device.
Laser diodes fabricated from II-VI semiconductor materials have been demonstrated by researchers at 3M in St. Paul, Minn. These devices emit radiation at about 520 nm at room temperature, a wavelength in the blue-green portion of the spectrum. They are disclosed generally in the Haase et al. article Short Wavelength II-VI Laser Diodes, Conference Proceedings for Gallium Arsenide and Related Compounds, 1991 Institute of Physics Conference Series, No. 120, pp. 9-16.
Buried-ridge (buried-heterostructure) laser diodes fabricated from III-V compound semiconductors such as GaAs and AlGaAs and emitting infrared light are well known and widely used. One of the first demonstrations of a buried-ridge III-V laser diode was reported by Tsukada in GaAs-Ga.sub.1-x Al.sub.x As Buried-Heterostructure Injection Lasers. J. Appl. Physics, Vol. 45, p. 4899 (Nov. 1974). These devices are fabricated using an epitaxial "regrowth" procedure by which the initial epitaxial structure is etched and then returned to a crystal growth apparatus to grow the lateral confinement layers (cladding). Epitaxial regrowth typically involves high substrate temperatures to desorb the oxides that form on the device when it is exposed to air after the etching step which forms the ridge.
The Iwano et al. U.S. Pat. No. 4,856,013 discloses a laser diode having an active layer and contact layer formed of III-V semiconductor compounds. The III-V semiconductor is etched to form a rib, and the rib buried in a confinement layer of II-VI semiconductor formed by metal organic chemical vapor deposition (MOCVD). The Niina et al. U.S. Pat. No. 4,607,369 discloses a semiconductor laser buried in a II-VI compound formed by a low temperature deposition process such as MOCVD. However, these epitaxial regrowth techniques are not feasible with II-VI devices since the desorption temperatures required would destroy the conductivity of the previously grown layers.
It is evident that there remains a continuing need for improved II-VI laser diode technology. For widespread commercial viability, the laser diodes must be relatively simple in construction and inexpensive to manufacture. The devices must also be capable of operating at relatively low threshold currents, and providing output beams of good optical quality.